Calculating Kₛₚ from Solubility


Water treatment plants, as you’ve learned in previous lessons, play a critical part in our lives. Water treatment and purification 🚰 are vital steps in providing safe drinking water 💧. Water purification for drinking and other purposes is a time-consuming procedure. Heavy metals must be eliminated, which is done with the help of carbonates and sulfates. Lead poisoning can cause serious health issues 🤒, especially in children under six. Because lead sulfates and carbonates are insoluble, they will readily precipitate out of the solution.

Is there a system to determine which compounds are soluble and which are not? Let’s assume we find out that the compound is soluble. The next question that may pop up in our minds is whether there is a system to find how soluble the substance is. Is it highly soluble or sparingly soluble? 🤔

ksp chemistry Source


The equilibrium constant for dissolving a solid material into an aqueous solution is the solubility product constant. Ksp is used to represent it. The solubility product is an equilibrium constant whose value is temperature-dependent. Due to increasing solubility, Kₛₚ normally rises as the temperature rises.


Assume you have barium sulfate and its saturated aqueous solution. The equilibrium between insoluble solids and ions is calculated using the following equation:

             BaSO₄(s) ⇌ Ba²⁺ (aq) + SO₄²⁻ (aq)

In the preceding scenario, the equilibrium constant is:

K = [Ba²⁺][SO₄²⁻]

In the situation of pure solid substances, the concentration stays unchanged; therefore, we may say:

Kₛₚ = K[BaSO₄] = [Ba²⁺][SO₄²⁻]


Here, Kₛₚ stands for the solubility product constant. It also means that when solid barium sulfate is in a steady state with its saturated solution, the products of barium and sulfate ion concentrations equal the solubility product constant. The Kₛₚ for a specific molecule may be calculated using solubility data. The steps below must be followed.

  1. Change solubility into molar solubility.
  2. Calculate the concentration of every ion in mol/L using the disintegration equation.
  3. Use the Kₛₚ equation.


  • The equilibrium constant for dissolving a solid material into an aqueous solution is the solubility product constant.
  • A compound’s solubility is measured in molarity (mol/L) and temperature-dependent.
  • The Kₛₚ indicates how soluble a chemical is. The greater the Ksp, the more solubility of the molecule is.


1. What Kₛₚ values would you expect for very insoluble compounds?

A compound’s solubility is measured in molarity (mol/L) and temperature-dependent. When a substance’s solubility is more than 1 g per 100 g of solvent, it is called soluble. When the solubility of a chemical would be less than 0.1 g per 100 g solvent, it is called insoluble.

2. What is the difference between solubility and solubility product constant?

The entire quantity of a chemical that could be dissolved or suspended at equilibrium is solubility. At the other extreme, the solubility product constant is an equilibrium constant that gives information on the equilibrium between the solid solute and its dispersed constituent ions throughout the solution.

3. What factors affect the value of Kₛₚ?

The following are some major elements that influence the solubility product constant:

  • The action of the common ion.
  • The ion-diversity effect.
  • There are ion-pairs available in the solution.

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  1. Calculating Ksp from Solubility. Accessed 18 Feb 2022.
  2. Solubility and Solubility Product. Accessed 18 Feb 2022.
  3. Conversion of Solubility to Ksp. Accessed 18 Feb 2022.

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